1). Field of the Invention
The present invention relates generally to testing of semiconductor chip packages and, more specifically, to a pickup chuck which is used for purposes of testing of multichip modules.
2). Discussion of Related Art
FIG. 1 of the accompanying drawings illustrates a conventional semiconductor chip package 10 which includes a package substrate 12 and a semiconductor chip 14 located on the package substrate 12. The semiconductor chip 14 comprises a circuit of logically integrated electrical elements, and a set of bond pads (not shown) on a surface thereof which allow the integrated circuit to be placed in communication with another device. An array of solder balls 16 are formed on the bond pads and the chip is located on the package substrate 12 with the solder balls contacting electric contact pads 18 on a front surface 20 of the package substrate 12. Another set of electric contact pads 22 are located on a back surface 24 of the package substrate 22 and electrical leads 26 extend through the package substrate 12, connecting the electric contact pads 18 and 22 to one another. It can thus be seen that the semiconductor chip 14 can be electrically accessed via the electric contact pads 22 on the back surface 24 of the package substrate 12.
Testing of the semiconductor chip 14 is usually done before shipping out of the package 10 by accessing the semiconductor chip 14 electrically via the electric contact pads 22, as hereinbefore described. The semiconductor chip 14 will fail if the operating temperature becomes too high. As a result, it is necessary that the manufacturer tests the chip 14 to ensure that the chip will operate properly within a certain temperature range of, for example, below a temperature of 110.degree. C. For that reason, testing is generally conducted under controlled conditions at the upper limit of the temperature range, the upper limit temperature being, for example, 110.degree. C. FIG. 2 illustrates diagrammatically a test setup 30 for testing the semiconductor chip package 10 and the semiconductor chip 14. The setup 30 includes a loading area 32, a chamber 34, an electrical test unit 36, a test head 38 on a wall of the chamber 34, and a device 40 for handling the semiconductor chip package 10 within the camber 34. The package 10 is first located within the load area 32 and then transported into the chamber 34 by means of a handler (not shown). The chamber 34 is maintained at the required temperature of 110.degree. C. by means of a heating element 42, and a thermometer, a thermostat or thermistor 44 is located within the chamber 34 for purposes of controlling the temperature within the chamber 34. The device 40 includes a pickup chuck 46 which picks the semiconductor chip package 10 up and transports it to the test head 38. The test head 38 includes a contactor 48 with a surface with an array of pogo pins (not shown) located thereon which make contact with the electric contact pads 22 on the back surface 24 of the package substrate 12. Electric leads 50 extend through the contactor 48 to the electric test unit 36. The semiconductor chip package 10 and the semiconductor chip 14, at the required temperature 110.degree. C., can now be tested with the electric test unit 36.
However, testing of the semiconductor chip package 10 and the semiconductor chip 14 may cause the chip to heat up to a temperature above the required test temperature 110.degree. C. This is undesirable as it will result in the scrapping of semiconductor chip packages which would operate reliably at the required test temperature of 110.degree. C. A pump 52 is located within the chamber 34 which extracts air from a thermal conditioning unit 53 which is maintained at 110.degree. C. by means of a heater 55, and provides the air to the pickup chuck 46 in order to maintain the semiconductor chip 14 at the required temperature of 110.degree. C. Heat is thus transferred from the semiconductor chip 14 to the air supplied by the pump 52. A special pickup chuck 46 is required for purposes of transferring the heat from the semiconductor chip 14 to the air.
FIG. 3 illustrates part of a pickup chuck 60 which is typically used for purposes of picking up the semiconductor chip package 10 and transferring heat therefrom.
The pickup 60 includes a body 62 with a channel 64 therethrough, a recess 66 for receiving the semiconductor chip package 10, a suction pad 68 within the recess 66 and a heat transferring member 70 which is secured to the body 60 by means of screw thread 72. The suction pad 68 is connected to a pipe 74 so that negative pressure within the pipe 74 causes the semiconductor chip package 10 to be retained within the recess 66. An ambiant or positive pressure within pipe 74 causes the semiconductor chip package 10 to be released from the pickup chuck 60. Small tubes 76 are positioned to blow the air supplied by the pump 52 into the channel 64. The heat transferring member 70 has a surface 78 which contacts the semiconductor chip 14, and a set of circular fins 80 within the channel 64. Any build up of heat within the semiconductor chip 14, when the semiconductor chip 14 is tested, is conducted through the heat transferring member 70 to the fins 80 from where it is convected to the air, supplied by the tubes 76, into the channel 64.
Recent technology developments have led to two or more semiconductor chips being located on a single package substrate, the chips and the package substrate having to be tested in unison. FIG. 4, for example, illustrates recent developments in a technology of Intel Corporation of Santa Clara, Calif. wherein a semiconductor chip package 88 is manufactured comprising a central processing unit (CPU) substrate 90 with a set of semiconductor chips 92 located on the CPU substrate 90. The semiconductor chip package 88 is located on a pin chassis 94 and a cover 96 is secured over the semiconductor chip package 88, the combination of which is then mounted to a motherboard (not shown) of a computer.
FIG. 5 illustrates the semiconductor chip package 88 comprising the CPU substrate 90 and the semiconductor chips 92A and 92B located thereon. The chip 92A is a processor, whereas the four smaller chips 92B typically comprise memory chips. The memory chips 92B are first located on an interposer substrate 98 which is then located on the CPU substrate 90. The interposer substrate 98 and the memory chips 92B have to be tested separately so that they can be separately scrapped upon failure. FIG. 6 illustrates the interposer substrate 98 with the memory chips 92B located thereon. FIG. 7 is a side view of the interposer substrate 98 with the memory chips 92B located thereon. It can now be seen that the pickup chuck 60 of FIG. 3 is insufficient for purposes of testing the semiconductor chip packages of FIGS. 5, 6, and 7, and that a pickup chuck is therefore required which can handle such semiconductor chip packages, called multichip modules (MCM's).
One feature of MCM's, in FIG. 8 is that the chips 92A and 92B have upper surfaces 100 which generally stand above an underlying package substrate 102 by different heights H1 and H2. It is therefore preferable that the pickup chuck can handle such MCM's.
Furthermore, as illustrated in FIG. 9, the MCM's usually bend during manufacturing. This is due to a cool down process used during manufacturing of the MCM and differences in thermal expansion of the package substrate 102 and the semiconductor chip 92. The problem of bending is more enchanced with MCM's because more chips 92 are carried by the substrate 102. It is therefore also preferable that the pickup chuck can handle such MCM's.
Furthermore, as illustrated in FIG. 11, some MCM's comprise components 104, mounted to the package substrate 102, that stand above the surface of the chips 92. It is therefore preferable that the pickup chuck can handle such MCM's.